The present invention relates to measuring fractional flow reserve (“FFR”) in a patient's vasculature. More specifically, the invention relates to a system and method for recovering and re-using a guidewire that is fitted with a sensor configured to measure FFR in a coronary vessel, where an initial attempt to use such an FFR guidewire was made and failed.
Fractional flow reserve is a technique used in coronary catheterization to measure pressure differences across a coronary artery stenosis (that is, a narrowing, usually due to atherosclerosis) to determine to what extent the stenosis impedes oxygen delivery to the heart muscle (myocardial ischemia).
Fractional flow reserve is defined as the pressure behind (distal to) a stenosis or lesion (identified herein as “Pd”) relative to the pressure before the stenosis, also known as aortic pressure (identified herein as “Pa”). The fractional flow reserve is obtained by dividing Pd by Pa. The result is an absolute number expressed as a fraction of unity. Thus, for example, an FFR of 0.80 means that a given stenosis causes a 20% drop in blood pressure. If there is no restriction of blood flow by a stenosis, the FFR value is 1.0 (or 100%). Thus, FFR gives some indication of the maximal flow down a vessel in the presence of a stenosis compared to the maximal flow in the hypothetical absence of the stenosis.
As used herein, the terms “FFR guidewire” and “pressure sensing guidewire” are used interchangeably to describe a guidewire that is fitted with a sensor for measuring pressure in order to compute fractional flow reserve.
FFR has certain advantages over other techniques for evaluating narrowed coronary arteries, such as coronary angiography, intravascular ultrasound, or CT coronary angiography. For example, FFR takes into account collateral flow, which can render an anatomical blockage functionally unimportant. Also, standard angiography can underestimate or overestimate narrowing, because it only visualizes contrast inside a vessel.
Other techniques can also provide information which FFR cannot. Intravascular ultrasound, for example, can provide information on plaque vulnerability, whereas FFR measurements are only determined by plaque thickness. Nevertheless, FFR allows real-time estimation of the effects of a narrowed vessel, and allows for simultaneous treatment with balloon dilatation and stenting. On the other hand, FFR is an invasive procedure for which non-invasive (less drastic) alternatives exist, such as cardiac stress testing in which physical exercise or intravenous medication is used to increase the workload and oxygen demand of the heart muscle, and ischemia is detected using ECG changes or nuclear imaging.